Question

What is the vertex form of `y= x^2 - 3x + 9`?

Answer 1

It is a minimum.

Explanation:

We're studying a trinomial, and we can tell wether its vertex is a minimum or a maximum only by looking at the sign of the coefficient of `x^2` which is here positive.

It's pretty visible on the graph that the derivative of this expression will first be negative, then become zero and then only be positive.

graph{x^2 -3x + 9 [-8.93, 11.07, 5.4, 15.4]}